Abstract

We studied the imaging performance of a chirped grating for a demultiplexer
designed for coarse wavelength division multiplexing using a wavefront aberration
analysis and the ray tracing simulation. The demultiplexer was composed of a chirped
grating, cylindrical lenses, and a waveguide. The best image point and the spot shape focused
by the chirped grating were effectively calculated with the wavefront aberration. We applied
the aberration analysis to design a waveguide to connect branched beams to photodetectors,
and we confirmed the demultiplexing performance experimentally.

Total wavefront aberrations, the third-order aberrations, and the residual error of the third-order
aberrations as a function of the position on the chirped grating: (a) Rc = 14.4 mm
(design configuration) and λ = 1.03λ0 and (b) Rc = 13.3 mm and λ = λ0.

Deformation of the focused spot of the chirped grating under the design configuration
condition: (a) the spot diagrams and (b) the spot width as a function of the wavelength calculated
with the third-order aberrations and the ray tracing.